What do you mean by different?
There is some difference in routing. The Silver Meteor follows the former Atlantic Coast Line main all the way from Richmond to Orlando to Auburndale, then the former Seaboard Air Line main from there to Miami. The Silver Star diverges from this route at Selma NC, takes the NS ex-Southern line to Raleigh, then the former SAL line from there to Savannah GA where it rejoins the ACL line. The Star also goes past Auburndale on the ACL on into Tampa and then turns around and goes back out to Auburndale and then down to Miami. Generally you will hear these lines referred to as the "A Line" and "S Line" as that is the way they are designated by CSX.
Most of the A Line is nominally 79 mph territory. The NS section is 59 mph and the S Line is I understand to be 60 mph north of Columbia SC and 79 mph south thereof, but I could be wrong on these. There are many more freight trains on the A Line.
Other differences I will leave to others.